The present invention is directed to a method for negative feedback controlling electrical power delivered to an electrical load, which method comprises generically, and as known to the skilled artisan, monitoring the electrical power delivered to the load, thereby generating a monitoring signal, forming in dependency of the monitoring signal and of a rated value signal a control deviation signal and adjustingxe2x80x94via a controller as e.g. a proportional or proportional-integral controllerxe2x80x94the electrical power delivered and monitored in function of the control deviation signal.
The present invention thereby departs especially from such method and power supply for delivering high power of at least 100 VA to a load.
It is an object of the present invention to provide such a negative feedback control method and, accordingly, such a negative feedback controlled power supply for superior accuracy of controlled power delivered to the load, with respect to a rated power value to be delivered.
Under a first aspect, the present invention departs from a method for negative feedback controlling electrical power delivered to an electrical load as mentioned above, whereat monitoring the electrical power delivered to the load results first in an analog monitoring signal, which is then analog to digital converted so as to result in a digital monitoring signal.
Under a second aspect, the present invention departs from a method for negative feedback controlling electrical power delivered to an electrical load as mentioned above, whereat adjusting the electrical power delivered to the load and monitoring is performed as a function of the control deviation signalxe2x80x94again via a respective controllerxe2x80x94by means of Pulse-Width Modulation (PWM).
In a method for negative feedback controlling electrical power, whereat the controlled value, namely the power delivered to the load, is digitalized as under the first aspect of the present invention, the overall accuracy of the negative feedback control significantly depends on the accuracy of the analog to digital conversion of the monitored signal. As is well known in the art of analog to digital conversion, noise of the analog input signal leads to digital output signal jitters by at least one least significant bit (LSB). This problem is customarily resolved by oversampling, i.e. by establishing a sampling rate which is considerably higher than necessitated by the spectrum of the analog signal to be converted. In fact, by oversampling, a multitude of digital samples are generated in a predetermined time frame, and the respective digitalized output value is formed by averaging the digital samples. Nevertheless, oversampling is always limited by the layout of a specifically considered converter not suited to handle sampling rates above a specific maximum rate. Rising the sampling rate over such limit makes it necessary to apply a differently designed A/D-converter which is often much more expensive and more critical to operate.
Under the generic object of the present invention as outlined above, and under the first aspect, it is therefore an object of the present invention to provide for an increased conversion accuracy of A/D-conversion of the monitoring signal, thereby avoiding the above mentioned drawbacks.
This object is inventively resolved by the method mentioned above and according to the preamble of claim 1, at which the analog monitoring signal is analog to digitally converted by performing the analog to digital conversion at least twice in parallel.
Thereby, at least two analog to digital converters, each construed for a predetermined sampling rate, are operated in parallel. This leads to an overall conversion with at least double that sampling rate, wherefore each of the converters is construed for, if both convertersxe2x80x94as preferredxe2x80x94are operated at equal sampling rates.
Under the second aspect of the present invention the following has to be considered: Whenever a method for negative feedback controlling electrical power delivered to an electrical load comprises adjusting the electrical power delivered to the load and monitored by means of PWM, accuracy of adjustment is significantly limited by the predetermined minimum pulse-width adjustment increment by which pulse length may be at all adjusted.
It is therefore a further object of the present invention, at a method as mentioned above, whereat, within the negative feedback loop, adjusting of the electrical power delivered to the load and monitored in function of the control deviation signal is performed by pulse-width modulation with a predetermined pulse repetition period, to improve adjustment accuracy beyond the limit set by the predetermined minimum pulse-width adjustment increment.
This object is resolved inventively and according to the characterizing part of claim 2 by calculating from the control deviation signal a desired pulse-width adjustment increment. Such a desired pulse-width adjustment increment will normally not accord with an integer multiple of the predetermined minimum pulse-width adjustment increment of the PWM considered. Therefore, and according to this second aspect of the present invention, a pulse of predetermined, preferably fixed length is not applied in every pulse repetition period, but only so often in time that, averaged over time, the adjustment by the integer multiple on one hand and/or the pulse accords with a pulse-width modulation adjustment with said desired pulse-width adjustment increment.
Thereby, one can exactly deal with any desired adjustment according to any fractions of the predetermined minimum pulse-width adjustment increment.
If e.g. the minimum predetermined pulse-width adjustment increment is of 30 nsec. and an actual control deviation would necessitate a pulse-width adjustment by an increment only of 10 nsec., then the calculation will reveal in preferred mode that the pulse of predetermined length (as in a most preferred embodiment a pulse which is the predetermined minimum pulse-width adjustment increment of 30 nsec.) is to be applied in every third pulse repetition period. This leads, time-averaged as by filtering, to the same result as applying a 10 nsec. pulse in every period of PWM.
If e.g. the control deviation signal reveals a desired pulse-width adjustment increment of 40 nsec., then there will be applied in each pulse repetition of the PWM one predetermined minimum pulse-width adjustment increment and, additionally, in every third period an additional predetermined minimum pulse-width adjustment increment, if, as in the most preferred mode, the pulse is selected to be just this increment.
In other words, this inventive technique combines customary pulse-width adjustment technique of PWM with a pulse frequency modulation (PFM) technique, at which pulses of a predetermined fixed length, namely as preferred according to the predetermined minimum pulse-width, are applied at a varying frequency.
According to the wording of claim 3, in a preferred embodiment of the inventive method and power supply both aspects of the invention as outlined above, namely of inventive A/D-conversion and of inventive adjustment by PWM and superimposed PFM, are combined.
Although the present invention under all its aspects may be used or realized for lower power supply, in a far preferred mode of operation, it is realized for controlling the electrical power of at least 100 VA delivered to a load. Monitoring the electrical power delivered to the load may be performed by monitoring the current or voltage delivered to the load.
In spite of the fact that the above mentioned A/D-conversion, at least twice in parallel, might be applied in cases, where both conversions are performed at minimum required sampling rates, additionally to the inventively performed parallel conversion, each of the A/D-conversions is performed with oversampling.
In spite of the fact that A/D-conversion in parallel could be performed in some cases at mutually different sampling rates, e.g. at sampling rates of integer ratio, A/D-conversions are performed in parallel at respective equal sampling rate.
Such an equal sampling rate may vary in time, in some applications, e.g. where the bandwidth development of an analog signal to be monitored is known in advance.
Nevertheless, in a preferred embodiment, parallel A/D-conversions are performed at respective equal and constant sampling rates. In a further preferred mode the converters are operated synchronously.
In a further preferred embodiment, each of the at least two parallel A/D-conversions is performed with a sampling rate of at least 100 kHz, thereby resulting in an overall sampling rate of two parallel conversions of 200 kHz.
Turning back to the present invention under its second aspect or under preferred combination of both of its aspects, in a preferred embodiment the pulse of predetermined lengthxe2x80x94applied by PFMxe2x80x94is selected to be the incremental pulse of the predetermined minimum pulse-width adjustment increment. Although this pulse needs not necessarily be of constant length, this is clearly the preferred mode.
Either the instantaneous control deviation may be corrected by an adjustment of the PWM pulse-width by an integer multiple of predetermined minimum pulse-width adjustment increments, or the instantaneous control deviation may only be accurately corrected by adjusting pulse-width modulation as was just explained and by additionally providing for applying pulses, preferably of the predetermined minimum pulse-width adjustment increments, by pulse frequency modulation, i.e. with a variable repetition rate, namely so often in time as necessary to deal with a control deviation which necessitate applying a PWM-adjusnnent by a fraction of the predetermined minimum pulse-width adjustment increment. Nevertheless, the case may also occur, where no pulse-width modulation adjustment at all is necessary, in these cases, namely for down to zero adjustments only, the single pulses, preferably of an extent according to the predetermined minimum pulse-width adjustment increment, are applied with the (modulatable) repetition rate set as necessary.
Thereby and in a further preferred mode, at the pulse frequency modulation, the accordingly modulated pulse repetition period is modulated by an integer multiple of the pulse repetition period of the pulse-width modulation.
For resolving the above mentioned object under the first aspect of the present invention there is further proposed a negative feedback control power supply. Under its second aspect a negative feedback control power supply resolves the above mentioned object, and in a preferred mode the objects under both of the aspects of the present invention are resolved by the digital negative feedback control power supply, which combines both aspects of the present invention.
Preferred embodiments of the inventive negative feedback control power supply under both its aspects will additionally become apparent from the following detailed description. Further, the inventive power supply, especially combining both aspects, is applied to magnet-supply of a synchrotron, thereby resulting in an inventive synchrotron system.